.NET 7 OutputCache Not Using Named Policies

I am trying to understand OutputCaching but I am running into some problems:

• Caching does work, but it's applying to all controller endpoints even if they don't have the attribute. I think this might be due to AddBasePolicy() but I'm more confused about my next point
• My named policy does not seem to be recognised on the GetElementCached method, the base policy of 5 second expiry always applies. If I remove the base policy caching does not work at all

I have registered the service and subsequently middleware as follows:

                .AddOutputCache(options =>
                {
                    options.AddBasePolicy(builder =>
                        builder.Expire(TimeSpan.FromSeconds(5)));

                    options.AddPolicy("DemoCache", builder =>
                        builder.Expire(TimeSpan.FromSeconds(20)));
                })

I have then created two controllers returning test data:

        [HttpGet("{index}/get-element-cache")]
        [OutputCache(PolicyName = "DemoCache")]
        [ProducesResponseType(typeof(string), StatusCodes.Status200OK)]
        public async Task<IActionResult> GetElementCached(int index)
        {
            return Ok(_myDb[index]);
        }

        [HttpGet("{index}/get-element-no-cache")]
        [ProducesResponseType(typeof(string), StatusCodes.Status200OK)]
        public async Task<IActionResult> GetElementNoCache(int index)
        {
            return Ok(_myDb[index]);
        }

I've checked worked examples and the documentation and I'm confused why my policy won't apply especially given the base policy works and can be changed making me believe I've configured it correctly.

> applying to all controller endpoints even if they don't have the
> attribute

Create policies when calling AddOutputCache to specify caching configuration that applies to multiple endpoints. A base policy provides default caching configuration for a collection of endpoints.You can read Configure multiple endpoints or pages to know more.

> My named policy does not seem to be recognised on the GetElementCached
> method,

I create an ASP.NET Core Web API project using the default template, before we add the basic caching, let’s run our app and hit the default Weather Forecast . We notice that each time we refresh, we get a different result. This is due to the default code randomizing the results.

Then make two small changes to Program.cs: add the output caching middleware to the service collection and request pipeline respectively. :

builder.Services.AddOutputCache(options =>
 {
     options.AddBasePolicy(builder =>
         builder.Expire(TimeSpan.FromSeconds(5)));

     options.AddPolicy("DemoCache", builder =>
         builder.Expire(TimeSpan.FromSeconds(20)));
 });
...
app.UseOutputCache();

Then test WeatherForecast to see the result,:

        [HttpGet("{index}/get-element-cache")]
        [OutputCache(PolicyName = "DemoCache")]
        [ProducesResponseType(typeof(string), StatusCodes.Status200OK)]
        public IEnumerable<WeatherForecast> GetElementCached()
        {
            return Enumerable.Range(1, 5).Select(index => new WeatherForecast
            {
                Date = DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
                TemperatureC = Random.Shared.Next(-20, 55),
                Summary = Summaries[Random.Shared.Next(Summaries.Length)]
            })
            .ToArray();
        }

        [HttpGet("{index}/get-element-no-cache")]
        [ProducesResponseType(typeof(string), StatusCodes.Status200OK)]
        public IEnumerable<WeatherForecast> GetElementNoCache()
        {
            return Enumerable.Range(1, 5).Select(index => new WeatherForecast
            {
                Date = DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
                TemperatureC = Random.Shared.Next(-20, 55),
                Summary = Summaries[Random.Shared.Next(Summaries.Length)]
            })
            .ToArray();
        }

Result: after we hit the URL again, we can see that the response is being cached for 20 seconds now :